Documentation
User documentation can be found on the OLM website.
Overview
This project is a component of the Operator Framework, an open source toolkit to manage Kubernetes native applications, called Operators, in an effective, automated, and scalable way. Read more in the introduction blog post and learn about practical use cases at the OLM website.
OLM extends Kubernetes to provide a declarative way to install, manage, and upgrade Operators and their dependencies in a cluster. It provides the following features:
Over-the-Air Updates and Catalogs
Kubernetes clusters are being kept up to date using elaborate update mechanisms today, more often automatically and in the background. Operators, being cluster extensions, should follow that. OLM has a concept of catalogs from which Operators are available to install and being kept up to date. In this model OLM allows maintainers granular authoring of the update path and gives commercial vendors a flexible publishing mechanism using channels.
Dependency Model
With OLMs packaging format Operators can express dependencies on the platform and on other Operators. They can rely on OLM to respect these requirements as long as the cluster is up. In this way, OLMs dependency model ensures Operators stay working during their long lifecycle across multiple updates of the platform or other Operators.
Discoverability
OLM advertises installed Operators and their services into the namespaces of tenants. They can discover which managed services are available and which Operator provides them. Administrators can rely on catalog content projected into a cluster, enabling discovery of Operators available to install.
Cluster Stability
Operators must claim ownership of their APIs. OLM will prevent conflicting Operators owning the same APIs being installed, ensuring cluster stability.
Declarative UI controls
Operators can behave like managed service providers. Their user interface on the command line are APIs. For graphical consoles OLM annotates those APIs with descriptors that drive the creation of rich interfaces and forms for users to interact with the Operator in a natural, cloud-like way.
Prerequisites
- git
- go version v1.12+.
- docker version 17.03+.
- kubectl version v1.11.3+.
- Access to a Kubernetes v1.11.3+ cluster.
Getting Started
Check out the Getting Started section in the docs.
Installation
Install OLM on a Kubernetes cluster by following the installation guide.
For a complete end-to-end example of how OLM fits into the Operator Framework, see the Operator Framework website and the Getting Started guide on OperatorHub.io.
Contributing your Operator
Have an awesome Operator you want to share? Checkout the publishing docs to learn about contributing to OperatorHub.io.
Subscribe to a Package and Channel
Cloud Services can be installed from the catalog by subscribing to a channel in the corresponding package.
Kubernetes-native Applications
An Operator is an application-specific controller that extends the Kubernetes API to create, configure, manage, and operate instances of complex applications on behalf of a user.
OLM requires that applications be managed by an operator, but that doesn't mean that each application must write one from scratch. Depending on the level of control required you may:
- Package up an existing set of resources for OLM with helm-app-operator-kit without writing a single line of go.
- Use the operator-sdk to quickly build an operator from scratch.
The primary vehicle for describing operator requirements with OLM is a ClusterServiceVersion. Once you have an application packaged for OLM, you can deploy it with OLM by creating its ClusterServiceVersion in a namespace with a supporting OperatorGroup.
ClusterServiceVersions can be collected into CatalogSources which will allow automated installation and dependency resolution via an InstallPlan, and can be kept up-to-date with a Subscription.
Learn more about the components used by OLM by reading about the architecture and philosophy.
Key Concepts
CustomResourceDefinitions
OLM standardizes interactions with operators by requiring that the interface to an operator be via the Kubernetes API. Because we expect users to define the interfaces to their applications, OLM currently uses CRDs to define the Kubernetes API interactions.
Examples: EtcdCluster CRD, EtcdBackup CRD
Descriptors
OLM introduces the notion of βdescriptorsβ of both spec and status fields in kubernetes API responses. Descriptors are intended to indicate various properties of a field in order to make decisions about their content. For example, this can drive connecting two operators together (e.g. connecting the connection string from a mysql instance to a consuming application) and be used to drive rich interactions in a UI.
See an example of a ClusterServiceVersion with descriptors
Dependency Resolution
To minimize the effort required to run an application on kubernetes, OLM handles dependency discovery and resolution of applications running on OLM.
This is achieved through additional metadata on the application definition. Each operator must define:
- The CRDs that it is responsible for managing.
- e.g., the etcd operator manages
EtcdCluster.
- e.g., the etcd operator manages
- The CRDs that it depends on.
- e.g., the vault operator depends on
EtcdCluster, because Vault is backed by etcd.
- e.g., the vault operator depends on
Basic dependency resolution is then possible by finding, for each βrequiredβ CRD, the corresponding operator that manages it and installing it as well. Dependency resolution can be further constrained by the way a user interacts with catalogs.
Granularity
Dependency resolution is driven through the (Group, Version, Kind) of CRDs. This means that no updates can occur to a given CRD (of a particular Group, Version, Kind) unless they are completely backward compatible.
There is no way to express a dependency on a particular version of an operator (e.g. etcd-operator v0.9.0) or application instance (e.g. etcd v3.2.1). This encourages application authors to depend on the interface and not the implementation.
Discovery, Catalogs, and Automated Upgrades
OLM has the concept of catalogs, which are repositories of application definitions and CRDs.
Catalogs contain a set of Packages, which map βchannelsβ to a particular application definition. Channels allow package authors to write different upgrade paths for different users (e.g. alpha vs. stable).
Example: etcd package
Users can subscribe to channels and have their operators automatically updated when new versions are released.
Here's an example of a subscription:
apiVersion: operators.coreos.com/v1alpha1
kind: Subscription
metadata:
name: etcd
namespace: olm
spec:
channel: singlenamespace-alpha
name: etcd
source: operatorhubio-catalog
sourceNamespace: olmThis will keep the etcd ClusterServiceVersion up to date as new versions become available in the catalog.
Catalogs are served internally over a grpc interface to OLM from operator-registry pods. Catalog data such as bundles are documented there as well.
Samples
To explore any operator samples using the OLM, see the https://operatorhub.io/ and its resources in Community Operators.
Community and how to get involved
Contributing
Check out the contributor documentation. Also, see the proposal docs and issues for ongoing or planned work.
Reporting bugs
See reporting bugs for details about reporting any issues.
Reporting flaky tests
See reporting flaky tests for details about reporting flaky tests.
License
Operator Lifecycle Manager is under Apache 2.0 license. See the LICENSE file for details.